Dave, gelcoat has a smooth shiney surface while fiberglass is not as smooth and shiney. You can see the fibers on the surface. I don't see why you couldn't use any wax on either as long as there is a UV protectant in it. I, however, use Meguiar's Glagship Premiun Marine Wax on my gelcoated Bighorn. It is formulated for gelcoat, has UV ray protection and is easy on and easy off. I apply it with an orbital polisher and buff with terry cloth. Hope this is the info you are looking for.
Peace
Dave